Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

Indolic secondary metabolites protect Arabidopsis from the oomycete pathogen Phytophthora brassicae

Abstract: The model plant Arabidopsis thaliana contains a large arsenal of secondary metabolites that are not essential in development but have important ecological functions in counteracting attacks of pathogens and herbivores.1,2 Preformed secondary compounds are often referred to as phytoanticipins and metabolites, that are synthesized de novo in response to biotic stress are known as phytoalexins.3 Camalexin is the typical phytoalexin of Arabidopsis. It has antimicrobial activity towards some pathogens and was shown to be an important component of disease resistance in several plant pathogen interactions.4 Glucosinolates (GS) are characteristic phytoanticipins of the Brassicaceae family including Arabidopsis. GS are best known as repellents or attractants for herbivorous insects and their predators whereas their antimicrobial potential has received relatively little attention.5 The GS are glucosides and the biologically active aglycone is released upon biotic stress by glucohydrolase enzymes commenly called myrosinases. Because an Arabidopsis mutant susceptible to the oomycete pathogen Phytophthora brassicae shows a partial deficiency in both camalexin and iGS accumulation we became intrigued by the role of these secondary compounds in disease resistance.6,7 Our results show that disease resistance of Arabidopsis to P. brassicae is established by the combined action of iGS and camalexin.

Suppression of bacterially-induced hypersensitive reaction and phytoalexin accumulation in bean by phaseotoxin

Abstract: PHASEOTOXIN is a trivial name given to an exotoxin produced by Pseudomonas phaseolicola, which causes halo blight of beans1. Although the mechanism of chlorosis induction in susceptible hosts is unknown, evidence indicates that chlorosis is casually related to inhibition of ornithine carbamoyltransferase (OCT; EC 2.1.3.3) by phaseotoxin, a potent and specific inhibitor of the enzyme2. Phaseotoxin may also be involved in the host specificity of the pathogen. We previously reported that in infected resistant bean plants (but not in infected susceptible ones) phaseotoxin production is suppressed in spite of substantial bacterial multiplication3. Further, in resistant beans treated with phaseotoxin, a larger number of bacteria are found than in non-treated plants4. These observations indicate that phaseotoxin may suppress the hypersensitive reaction (HR) in resistant hosts. The object of this study was to investigate whether pretreatment of resistant cultivars of bean with phaseotoxin suppresses the HR response of the host and phytoalexin accumulation on subsequent inoculation with P. phaseolicola, and our results seem to support this.

Host-Pathogen Interactions : XXI. Extraction of a Heat-Labile Elicitor of Phytoalexin Accumulation from Frozen Soybean Stems.

Abstract: An extract of frozen and thawed soybean (Glycine max L. Merr. cv. Wayne) stems is active, in wounded soybean cotyledons, as a heat-labile elicitor of phytoalexins. The elicitor activity of the extract is destroyed by heating to 95°C for 10 minutes. The fraction that contains heat-labile elicitor activity releases heat-stable elicitor-active molecules from purified soybean cell walls. Heat-labile elicitor activity voids a Bio-Gel P-6 column and can be absorbed onto and eluted from a DEAE Sephadex ion exchange column. Using the cotyledon phytoalexin elicitor assay, maximum heatlabile elicitor activity was obtained when soybean stems were extracted with acetate buffer at pH 6.0. Addition of 1 millimolar CaCl2 increased apparent heat-labile elicitor activity. The heat-labile elicitor stimulated maximum phytoalexin accumulation when applied to cotyledons immediately after the cotyledons were cut. Partially purified stem extracts lost heat-labile elicitor activity during storage for several days at 3°C. The possible role of a heat-labile elicitor in stimulation of phytoalexin accumulation by both abiotic and biotic elicitors is discussed.